Question: Before the previous stop there were 27 people riding on a train. 4 people ended up getting off at the stop. How many people are riding the train now?
Explanation: The number riding the train now is the difference between the number who were riding and the number who got off at the previous stop. The difference is $27 - 4$ people on the train. $27 - 4 = 23$ people are on the train.